gas: sframe: fine tune the fragment fixup for SFrame func info
SFrame function info is an unsigned 8-bit field comprising of the following (from LSB to MSB): - 4-bits: FRE type - 1-bit: FRE start address encoding - 3-bits: Unused At the moment, the most-significat 4-bits are zero (The FRE start address encoding of SFRAME_FDE_TYPE_PCINC has a value of zero, and the upper 3-bits are unused). So the current implementation works without this patch. To be precise, however, the fragment fixup logic is meant to fixup only the least-significant 4-bits (i.e., only the FRE type needs to be updated according to the function size). This patch makes the gas implementation a bit more resilient: In the future, when the format does evolve to make use of the currently unused 3-bits in various ways, the values in those 3-bits can be propagated unchanged while the fragment fixup continues to update the lowermost 4-bits to indicate the selected FRE type. ChangeLog: * gas/gen-sframe.c (create_func_info_exp): New definition. (output_sframe_funcdesc): Call create_func_info_exp. * gas/sframe-opt.c (sframe_estimate_size_before_relax): The associated fragment uses O_modulus now. (sframe_convert_frag): Adjust the fragment fixup code according to the new composite exp.
This commit is contained in:
Indu Bhagat
parent
3f107464e3
commit
989aabcb56
@ -396,8 +396,8 @@ sframe_get_fre_offset_size (struct sframe_row_entry *sframe_fre)
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- <val> and <width> are themselves expressionS.
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- <val> stores the expression which when evaluated gives the value of the
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start address offset of the FRE.
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- <width> stores the expression when when evaluated gives the number of
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bytes needed to encode the start address offset of the FRE.
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- <width> stores the expression when evaluated gives the number of bytes
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needed to encode the start address offset of the FRE.
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The use of OP_absent as the X_op_symbol helps identify this expression
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later when fragments are fixed up. */
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@ -431,6 +431,41 @@ create_fre_start_addr_exp (expressionS *cexp, symbolS *fre_pc_begin,
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cexp->X_add_number = 0;
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}
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/* Create a composite exression CEXP (for SFrame FDE function info) such that:
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exp = <rest_of_func_info> OP_modulus <width>, where,
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- <rest_of_func_info> and <width> are themselves expressionS.
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- <rest_of_func_info> stores a constant expression where X_add_number is
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used to stash away the func_info. The upper 4-bits of the func_info are copied
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back to the resulting byte by the fragment fixup logic.
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- <width> stores the expression when evaluated gives the size of the
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funtion in number of bytes.
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The use of OP_modulus as the X_op_symbol helps identify this expression
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later when fragments are fixed up. */
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static void
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create_func_info_exp (expressionS *cexp, symbolS *dw_fde_end_addrS,
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symbolS *dw_fde_start_addrS, uint8_t func_info)
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{
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expressionS width;
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expressionS rest_of_func_info;
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width.X_op = O_subtract;
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width.X_add_symbol = dw_fde_end_addrS;
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width.X_op_symbol = dw_fde_start_addrS;
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width.X_add_number = 0;
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rest_of_func_info.X_op = O_constant;
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rest_of_func_info.X_add_number = func_info;
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cexp->X_op = O_modulus;
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cexp->X_add_symbol = make_expr_symbol (&rest_of_func_info);
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cexp->X_op_symbol = make_expr_symbol (&width);
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cexp->X_add_number = 0;
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}
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#endif
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static void
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@ -538,19 +573,17 @@ output_sframe_funcdesc (symbolS *start_of_fre_section,
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out_four (sframe_fde->num_fres);
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/* SFrame FDE function info. */
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#if SFRAME_FRE_TYPE_SELECTION_OPT
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expressionS width;
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width.X_op = O_subtract;
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width.X_add_symbol = dw_fde_end_addrS;
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width.X_op_symbol = dw_fde_start_addrS;
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width.X_add_number = 0;
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frag_grow (1); /* Size of func info is unsigned char. */
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frag_var (rs_sframe, 1, 0, (relax_substateT) 0,
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make_expr_symbol (&width), 0, (char *) frag_now);
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#else
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unsigned char func_info;
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func_info = sframe_set_func_info (SFRAME_FDE_TYPE_PCINC,
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SFRAME_FRE_TYPE_ADDR4);
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#if SFRAME_FRE_TYPE_SELECTION_OPT
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expressionS cexp;
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create_func_info_exp (&cexp, dw_fde_end_addrS, dw_fde_start_addrS,
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func_info);
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frag_grow (1); /* Size of func info is unsigned char. */
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frag_var (rs_sframe, 1, 0, (relax_substateT) 0,
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make_expr_symbol (&cexp), 0, (char *) frag_now);
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#else
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out_one (func_info);
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#endif
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}
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@ -40,10 +40,10 @@ sframe_estimate_size_before_relax (fragS *frag)
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The two kind of fragments can be differentiated based on the opcode
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of the symbol. */
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exp = symbol_get_value_expression (frag->fr_symbol);
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gas_assert ((exp->X_op == O_subtract) || (exp->X_op == O_absent));
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gas_assert ((exp->X_op == O_modulus) || (exp->X_op == O_absent));
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/* Fragment for function info in an SFrame FDE will always write
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only one byte. */
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if (exp->X_op == O_subtract)
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if (exp->X_op == O_modulus)
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ret = 1;
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/* Fragment for the start address in an SFrame FRE may write out
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1/2/4 bytes depending on the value of the diff. */
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@ -92,8 +92,12 @@ sframe_convert_frag (fragS *frag)
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offsetT fsize;
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offsetT diff;
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offsetT value;
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unsigned char func_info = SFRAME_FRE_TYPE_ADDR4;
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offsetT rest_of_data;
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uint8_t fde_type, fre_type;
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expressionS *exp;
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symbolS *dataS;
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symbolS *fsizeS, *diffS;
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/* We are dealing with two different kind of fragments here which need
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@ -103,19 +107,29 @@ sframe_convert_frag (fragS *frag)
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The two kind of fragments can be differentiated based on the opcode
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of the symbol. */
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exp = symbol_get_value_expression (frag->fr_symbol);
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gas_assert ((exp->X_op == O_subtract) || (exp->X_op == O_absent));
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gas_assert ((exp->X_op == O_modulus) || (exp->X_op == O_absent));
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/* Fragment for function info in an SFrame FDE. */
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if (exp->X_op == O_subtract)
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if (exp->X_op == O_modulus)
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{
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fsizeS = frag->fr_symbol;
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/* Gather the existing value of the rest of the data except
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the fre_type. */
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dataS = exp->X_add_symbol;
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rest_of_data = (symbol_get_value_expression(dataS))->X_add_number;
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fde_type = SFRAME_V1_FUNC_FDE_TYPE (rest_of_data);
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gas_assert (fde_type == SFRAME_FDE_TYPE_PCINC);
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/* Calculate the applicable fre_type. */
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fsizeS = exp->X_op_symbol;
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fsize = resolve_symbol_value (fsizeS);
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if (fsize < SFRAME_FRE_TYPE_ADDR1_LIMIT)
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func_info = SFRAME_FRE_TYPE_ADDR1;
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fre_type = SFRAME_FRE_TYPE_ADDR1;
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else if (fsize < SFRAME_FRE_TYPE_ADDR2_LIMIT)
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func_info = SFRAME_FRE_TYPE_ADDR2;
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fre_type = SFRAME_FRE_TYPE_ADDR2;
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else
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func_info = SFRAME_FRE_TYPE_ADDR4;
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value = func_info;
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fre_type = SFRAME_FRE_TYPE_ADDR4;
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/* Create the new function info. */
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value = SFRAME_V1_FUNC_INFO (fde_type, fre_type);
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frag->fr_literal[frag->fr_fix] = value;
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}
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